Method of making molds



D. L. JOCELYN METHOD OF MAKING MOLDS Aug. 16, 1949.

2 Sheets-Sheet 1 Filed 0G12. 25, 1945 &\\

IN VEN TOR.

Aug. La, 1949.y

Filed oct. 25, 1945 D. L. JOCELYN METHOD 0F MAKING MOLDS 2 Sheets-Sheet2 f24 if ///'//1 INVENTOR.

Patented Aug. 16, 1949 PATET oFFlCE This invention relates to molds foruseV in the production of cast or molded articles and particularly toso-called permanent type molds which may be used repeatedly for theproduction of relatively large numbers of castings in the same mold. Animportant object of the invention is to provide a metallic mold which ispermeable in character thereby permitting the rapid escape of gases fromthe mold cavity during the casting operation and as a consequenceenabling superio castings or molded articles to be made. A furtherobject of the invention is to provide a sintered metal mold formed ofpowdered metal which, before sintering, is pressed through the medium-ofdies under great pressure to produce the casting cavity, the mold havingsubstantially all of the advantages of a conventional permanent moldyet'capable of being produced at a fraction of the cost theerof, thusenabling many articles to be cast by permanent mold methods whichotherwise would not be possible owing to the great cost of conventionaltype permanent molds.

Still another object of the invention is to provide a sintered powderedmetal mold which is self-venting due to the permeability thereof andwhich is thus capable of producing a casting having a smoother surfacethan ordinary molds.

A further object of the invention is to provide a permanent metal moldof relatively inexpensive character in which the portions of the moldhaving the casting cavity or cavities are formed of and having a highdegree of uniformity in the y density of the walls of the mold.

Still another object of the invention is to produce a powdered metalfoundry mold of substantially uniform density for casting an article ofirregular contour, such as an article having protruding bosses `orstepped portions forming different levels, as a result of which uniformdensity and freedom from distortion during heat treatment of the moldbrlquette are not possible by the use of conventional methods of formingthe -briquette from powdered metal. AIn accordance with the presentinvention, however, I introduce into the die cavity containing the looseor un.

compacted powdered metal one or more preformed briquettes of powderedmetal which has been partially compressed to predetermined density, thepre-formed -briquettes of required size andshape being positioned in thedie cavity at localities where different levels are present in thepunch. Upon compression of the material between upper and lower punchesthe pre-formed briquettes' are consolidated with the powdered mass andaugment the density of the final briquette at the localities wherevariations in density would otherwise occur due to the different levelson the punch. Thus, by the use of these preformed briquettes it ispossible to compensate for variations in density which otherwise wouldoccur in the formation of a powdered metal mold.

A further object of the invention is to produce a powdered metal moldhaving sumcient permeability to cause the mold to be self-venting duringthe casting operation, and invaddition to provide a metallic surfacingof chromium, or other high heat resistant metal, on the mold permittingmolten metals to be poured at higher temperatures in the mold whilereducing the tendency of the pores of the mold to become closed orblocked as the result of fusing of the surface of the mold in contactwith the molten metal. Such metallic surfacing of the mold renders themold highly wear resistant and more durable while at the same timeproviding a smoother, harder surface capable of producing smoothersurfaces on the castings.

This application is a. continuation in part of my application Serial No.572,117, filed January 10, 1945, now abandoned.

Other objects of this invention will appear in the following descriptionand appended claims, reference being had to the accompanying drawingsforming a part of this specication wherein like reference chaarctersdesignate corresponding parts in the several` views.

Fig. 1 is a side elevation of a mold unit or section constructed inaccordance with the present invention, this view being takensubstantially through lines I-I of Fig. 2 looking in the direction ofthe arrows.

Fig. 2 is an enlarged section of the assembled mold units or sectionstaken substantially through lines 2-2 of Fig. 1 looking in the directionof the arrows.

Fig. 3 is a sidevelevation of the assembled mold shown in Fig. 2.!

Fig. 4 is a fragmentary sectional view of a punch and die apparatus forforming the powdered metal mold unit.

Fig. 5 is a view similar to Fig. 4 illustrating the position of theupper punch at the commencement of a pressing operation.

Before explaining in detail the present infention it is to be understoodthat the invention is not limited in its application to the details ofconstruction and arrangement of parts illustrated in the accompanyingdrawings, since the invention is capable of other embodiments and ofbeing practiced or carried out in various ways. Also it is to beunderstood that the phraseology or terminology -employed herein is forthe purpose of description and not of limitation.

It will be understood that the invention is capable of use in casting ormolding a wide variety of articles from dierent materials. principallymetal and its alloys, thermoplastics and thermosetting resins. Anysuitable number of articles may be cast simultaneously in the same moldand in the present embodiment I have shown a mold constructed to casttwo articles, each of which is cast in a mold cavity formed partly inone mold section, such as the cope, and partly in the other moldsection, such as the drag.

In the drawings, wherein one embodiment is illustrated by way ofexample, the mold comprises two sections I and II, preferably in theform of cast iron blocks, assembled along a lpart-- ing line I2. Theblock II) is provided with a pair of similar bores I3 and in like mannerthe block I I is provided with a pair of bores I4. These borespreferably extend entirely through the supporting blocks III and II, thebores I3 being adapted to receive. cylindrical powdered metal moldinserts I and the bores I4 being adapted to receive cylindrical powderedmetal mold inserts I 6. The corresponding pairs of mold inserts I5 andI6, when positioned within their respective bores, meet at the commonparting line I2. In the present instance, each mating pair of -powderedmetal mold inserts I5 Aand I6 are formed to provide a common castingcavity C, as shown in Fig. 2. As hereinafter described, the mold insertsare formed of sintered powdered metal such as ferrous metal or an alloythereof, and the cavities C are shaped so as to produce the desiredarticles when the molten metal congeals within the cavities after thepouring operation. In the present instance, each insert I6 is formedwith a portion I1 of a riser extending upwards from the cavity andcommunicating therewith. Each riser portion I1 communicates with a riserportion I8 formed in the supporting block I I for the inserts I6. Alsoeach mold insert I6 is formed with a portion I8 of a runner gate leadinginto the cavity C from below.

The supporting block II is cast or otherwise fabricated to providediverging runner gate portions 20, as clearly shown in Fig. l, registerwith which leads upwards to the sprue passage 22 into which the moltenmetal is poured. The gateportions 20, as clearly shown in Fig. 1,registers with the gates I9 through which the metal enters the cavitiesC.

The powdered metal mold inserts I5 and I6 have a smooth sliding fitwithin their respective bores I3 and I4 in the supporting blocks I IIand II. Thus, when assembling the mold, the mold inserts will slidecinto the bores until flush with the inner upright faces of the blocksI0 and II 4 l at the parting line I2. They are then rigidly clamped inplace by means of retainer bolts 23 extending through tapped holes inthe blocks III and II and engaging the inserts. The blocks Il! and II,with their assembled mold sections. are then assembled as illustrated inFig. 2, being clamped together in tight abutting relation at the partingline I2 in any conventional mannen after which the castings are poured.lSuitable knock-out pins (not shown) of any conventional kind may bemounted in the inserts I5 and I6 for ejecting the castings after themold sections have been separated. Thereafter the riser and gateportions of the castings are removed to -provide the finished article.

The mold inserts I5 Yand I6 are prepared from powdered metal, preferablyferrous metal or an alloy thereof, and are shaped under high pres- 'sureand then sintered. In Figs. 4 and 5 there is illustrated a pressdesigned for the purpose of forming the mold inserts I5, it beingunderstood that the mold inserts I5 will be formed in substantially thesame manner as the inserts I5. As illustrated in Figs. 4 and 5, thepress herein utilized to prepare the powdered metal mold insertscomprises a bed or bolster 2l and a side die 25 supported upon the bedby means of removable blocks 26. The die 25 has a central vertical bore21 corresponding in diameter to the bore I3 or I4 in the mold Supportingblock III or II.- Suitably anchored to the bed 2l of the press Ais alower punch 28 having a vertically extending cylindrical portion fittinginto the bore 21 in the die 25 and in the present instance terminatingin a flat top surface 29. The press also comprises an upper vertically'reciprocable punch 30 of a diameter to have a sliding t within the bore21 of the side die 25. The working end of this punch is shaped toproduce, in cooperation with the bottom punch and side die, the powderedmetal mold insert I5 with its portion of the casting cavity C.Accordingly, the punch has an annular surface 3l which produces thatportion of the mold insert I5 lying along the parting line I2. 'I'henose of the punch, which protrudes downwardly below the surface 3i, isformed with sections 32, 33 and 34 which lie at diierent levels, theportions 32 and 33 vlbeing joined by an upwardly curving or inclinedsurface 35. a

In order to obtain as high a degree of accuracy as possible in respectto shape and dimensions of the casting cavity C, it is important thatthe.

cavity'in the insert will also have these corre-v sponding levels, asindicated by the levels 32, 33 and 34 in Figs. 4 and 5. If it isattempted to prepare the mold insert by compressing a mass of powderedmetal introduced between the punches 28 and 30, the powder at thedifferent levels of the punch 30 will be pressed under differentpressures and the densities of the compressed powder willcorrespondinglyvary. In other words, uti-` lizing the punch 30 shown inFigs. 4 and 5, the powdered metal after compression would normally becompacted to the greatest extent so as to produce the greatest densityopposite the' highest level 32 of the punch. The density of the powderedm'etal would decrease opposite the curved surface and would beincreasingly less opposite the successive lower levels 33, 34 and 3| inproportion to the distances of these levels from the level 32. Thus, inthe absence of mold compensating means in accordance with the presentinvention for increasing the density of the powdered metal opposite thedifferent levels 3|, 33, 34 and 35, the finally compressed powdered moldwould have widely varying densities and would not produce a satisfactorymold after the sintering operation. This variation in compactness anddensity arises from the fact that the metal powder will not flow underpressure as in the case of flowable or plastic materials, and hence, thecompression of the powder opposite different levels of the punch willvary.

According to the present invention, therefore, I obtain a high degree ofuniformity in density of the pressed metal powders by compensating CIIfor the lower levels in the punch through the medium of pre-formedpowdered metal briquettes. These briquettes are pre-compressed to thedesired extent and are so dimensioned that they may be positioned withinthe die before the pressing operation commences and arranged oppositeand coextensive with the lower levels of the punch so as to increase thedensity of the final mold to the desired extent. Thus, as illustrated inFigs. 4

and 5, an annular or ring-shaped pre-compressed powdered metal briquette3l is positioned opposite the annular flat surface forming the lowestlevel 3| in the punch 30. A pre-compressed powdered metal briquette 38is positioned opposite the surface forming the next lower level 34, theadjacent surfaces of briquette 38 and level 34 being coextensive. Apre-compressed powdered metal briquette 39 is positioned opposite thenext lower level 33, and a pre-compressed briquette is positionedopposite the curved level 35, the adjacent surfaces of these briquettesand the associated portions of the punch being coextensive.

With the lower punch 28 and die 25 positioned in the press asillustrated in Fig. 4, and the upper punch 30 retracted, a mass ofpowdered metal 4| is introduced into the bore 21 ov'er the lower punch,the level of ll of the powder being indicated by the line 42. Thereafterthe pre-formed and pre-compressed powdered metal briquettes 31-40 lareembedded in the powder 4| and arranged opposite the various levels ofthe punch 3D, as clearly illustrated in Fig. 4. After the preformedbriquettes have been properly positioned and firmly embedded in thepowder, an additional small amount of metal powder may be sprinkled overthe briquettes in order to ll any crevices, cracks or voids therebetweenand provide a slight covering therefor. Thereupon the upper punch 30 iscaused to descend so as to position the same in the shaped cavity formedbetween the pre-formed briquettes 31-40 and the intervening level ofpowder 42, as in the manner shown in Fig. 5. With the lower punch instationary position on the bed 24 and the die 25 in like mannersupported on the removable blocks 26, the descent of the'upper punch iscontinued so as to apply pressure and compress the powders, resulting inconsolidating the pre-formed briquettes intimately and homogeneouslywith the mass of loose powder 4|. Thereupon the pressure of the upperpunch is released to permit removal of the blocks 26, after which theupper punch is caused to descend again. Inasmuch as the die 25 at thistime is unsupported it will move in unison with the upper punch relativeto the lower punch 28 thereby resulting in upward pressure being exertedby the stationary lower punch against the bottom of the compressedbriquette equalizing the density of the powder. The briquette thuscompressed under predetermined pressure will be of substantially uniformdensity throughout and may thereafter be heat treated or sintered toproduce the nal mold unit I5 Without danger of any appreciable buckling,warping or distortion. It will be understood that the mold unit 16 orany other selected mold unit or section may be produced in accordancewith the foregoing described method utilizing pre-compressed briquettesat regions where variations in levels exist so as to increase the amountof powder at these regions and compensate for variations in density ofthe compressed powdered metal which otherwise would occur by the use ofconventional methods.

It will be manifest that the dimensions as to width, height and shape ofthe pre-compressed or pre-formed briquettes 31-38 will be governed bythe dimensions of the low level areas of the upper punch, or thecomplementary areas of the article being formed, as well as thedifferences in height of the several levels. The densities of theprecompressed briquettes may of course vary but should be selected inadvance in order to determine the correct heights or thicknesses in avertical direction of the briquettes. The amount of pre-compression ofthe powder' to form the briquettes 31-39 should preferably be such as togive as low a density as possible while permitting safe handling thereofwithout disintegration or crumbling of the briquette. Assuming that theselected density of the finally compressed -mold is on the order ofgrams per cubic centimeter, and

the compression ratio is approximately three tol one, the pre-formedbriquette may be satisfactorily formed with a density on the order ofapproximately 70 grams per cubic centimeter. The height or verticalthickness of the briquette may be readily calculated by the followingformula:

where D1 is the desired density of the final briquette, D2 is theselected density of the pre-formed briquette 31, 38, 39 or 40; H is thedistance between the highest level and the level opposite which thebriquette is to be placed; and T is the vertical thickness of thepre-formed briquette.l Assuming that 'the distance between levels 3| and32 is three inches, and using the density values mentioned above by wayof example, then the vertical thickness of briquette 3l would becalculated as follows: f

g-X 3= 4.07 inches It will be understood that the densities of thepre-formed briquettes may be varied to suit condit-ions and that smallamounts of suitable binders, such as sugar water, syrup or any othermaterial which on heat treatment will char or reduce to a harmlesscarbon residue, may be added to the metal powder in order to facilitatehandling of the pre-formed briquettes. Irregular Aor odd shapes ofpre-formed briquettes may be formed in suitably shaped dies or may becut from pre-formed plates, slabs, cylinders, rings, etc.

From the foregoing it will be seen that substantially uniform densitydistribution, equalization of strength throughout all sections of thennal briquette, freedom from distortion during heat treatment orsintering, and greater accuracy in detail of contour and shape areachieved by virtue of the present invention. As a consequence the moldsI5 and I6 produced from sintered briquettes ln accordance with thepresent method will not only be highly permeable but will be stronger,more durable and lasting and more accurate in all respects.

Although castings produced in ferrous metal molds embodying the presentinvention will have relatively smooth surfaces free from excessivepitting, even superior results may be achieved by providing a metallicsurfacing or coating over the inner surfaces of the molds I5 and yI6. Athin film of chromium, or other high heat resistant metal, is depositedover the mold surfaces by ordinary electrolytic procedure. However, thedeposition of the chromium is conducted so as to eliminate theabsorption of hydrogen by the metal which, in carrying out the4 process,is in effect de-hydrogenated. 'I'he chromium film will not obstruct orIclose the minute pores which permeate the mold but instead form thinprotective walls or layers around the pore openings at the surface ofthe mold, and due to its high heat resistance properties will preventover prolonged periods of use any tendency of the metalpf the mold tofuse at the surface thereof and close oif the pore openings. The poresin the surface of the chromium film provide a multitude of tinyexpansion areas enabling the chromium film to expand and contractsufdciently to resist cracking, aking or peeling during the castingoperation. A chromium surface powdered ferrous metal mold in accordancewith the present invention may be used advantageously for castingvarious metals, such as' aluminum and brass. In fact, highly successfulresults have been obtained in making repeated runs of steel castings ina powdered ferrous metal mold surfaced with chromium. Even though themolten steel was poured at a temperature on vthe order of 2800 F. nodestructive effects on the surface of the mold were discerned.

I claim:

1. The method of making a powdered metal mold utilizing a forming punchcontoured with different levels, including the steps of supporting aloose mass of powdered metal in a confined space opposite said punch,positioning a pre-compressed powdered metal briquette in said massopposite a lower level of the punch, and consolidating said mass andbriquette together by pressure exerted vthereon by said punch.

2. The method of making a powdered metal mold utilizing a forming punchcontoured with diierent levels, including the steps of supporting aloose mass of powdered metal in a confined space opposite said punch,positioning a plurality of pre-compressed powdered metal briquettes ofdifferent thicknesses in said mass opposite the different lower levelsof the punch, and consolidating said mass and briquettes by pressure ofthe punch.

DOUGLAS L. JOCELYN.

REFERENCES CITED The following references are of record in the file ofthis patent:

UNITED STATES PATENTS Number Name Date 1,809,872 Solderberg June 16,1931 2,042,635 Schellens June 2, 1936 2,048,222 Rehmann July 21, 19382,121,448 Ritzau June 21, 1938 2,298,885 Hull Oct; 13, 1942 1 2,299,192Tormyn Oct. 20, 1942 2,397,831 Bellamy Apr. 2, 1948 FOREIGN PATENTSNumber Country Date 330,018 Great Britain June 5, 1930

